With "flatish water - typically gusty 6 to 15 knots" as described above, for the HS133 replacement, I would say go for the iSonic 135 or the iSonic 145 (Former F-Type 138). You could even go for the iSonic 155 if you added a 9.5 or 10.0, and gain alot of early planing.
I have an F-Type 148, use it with 9.5/8.5/7.3.
Jibing is similar to formula boards but much less stiff, but still requires that "wide board" technique. But early planing capabilities are fantastic.
If you did the 145, I bet you could get away with 8.5/6.5 (6.5 when the water is still not too choppy) and get something smaller for when the chop picks up (like the iSonic 105 as you suggest above) for 5.5/6.5.
Or you could go with something like a Kombat if you want better manuevering/jibing, but not one of the smaller ones as PG suggest above, at 5.5/6.5 a 107 or 97.
My middle board is iSonic 125 (lots of overlap with my F-Type 148, I know and I like it that way) and smallest is Carve 122 which I plan to swap for a Kombat 97 in the spring.
Nice of Starboard to give us so many good boards to choose from!